It is known that small (0.5-20.0 micron) inhaled inorganic particles normally reach the alveolar ducts and air spaces. There the particles confront various components of the alveolar wall, such as surfactant, epithelial cells, and alveolar macrophages. The initial events of particle interaction with these structures are poorly understood and relate directly to how certain particulates are distributed in the lung and exert their toxic influences. We have found that after one hour inhaled chrysotile asbestos is found exclusively in the small air spaces. After one day of exposure, fibers are found in alveolar macrophages, and after five days asbestos reaches the alveolar epithelium, interstitium, and capillary spaces. Apparently, inhaled asbestos reaches the connective tissue compartment of the lung by inter-or intraepithelial particle transport.